Choosing the right blade is perhaps the most important factor in determining the success of a sawing job. Whether it’s quality cuts or fast throughput that’s needed, putting the right blade on a saw ranks high – but it’s not the only thing that matters. From lubricant and coolant to blade speed to downfeed to controlling vibration, everything needs to be considered to obtain the desired outcome.
Experienced saw operators know the telltale signs of something gone awry. For example, Pat Schmidt, regional sales manager, DoAll Sawing Products, says listening to the saw while it is cutting can help determine downfeed issues.
“A high-pitched squeal can also be a leading factor when listening to the cut,” Schmidt says, “indicating too light of a feed rate for the blade speed being applied. There is also the possibility of work-hardening the material being cut by having a light feed rate and not pulling a chip.”
Speaking of chips, which are the fragments of material left behind as the blade works through the material, Dan Fernandes, senior product marketing manager, Lenox, says evaluating chips is another method of determining if the downfeed is too low or high.
“If chips are thin or powdered,” Fernandes says, “the operator needs to increase the feed rate. If chips are burned or heavy, the operator needs to decrease the feed and speed. For the optimum feed rate when cutting, operators should target curled, silvery and warm chips.”
Lenox’s SawCalc can assist in this area. It’s an online calculator where operators can enter the variables of a job and get information on how to make more effective cuts.
Jerry Kroetch, president of Scotchman Industries, says there’s almost an art to dialing in downfeed settings. Going too low on the downfeed can result in work-hardened material, making it tougher for the blade to get through. However, Kroetch says cutting with too high of a downfeed, “can stall the blade motor and break a blade.”
For example, with cold saws where the blade is circular, too much pressure can cause “pick-up,” where the material being cut bonds to the sides of the teeth on the blade, which makes the tooth wider or thicker than the blade. Each time a wider tooth passes through the material, it grabs and makes the saw head jump, causing a “clunk, clunk, clunk” sound. The blade will eventually jam.
“Over time, the operator learns how to set the feed rate by sound and how it feels during the cut process,” Kroetch says.
Wren Gibbs, blade specialist at DoAll Sawing Products, says bandsaw operators also need to look out for low vibration, which is a common sign of a feed rate that is too high, resulting in pulling large chips and the risk of blade failure.
“The squeal is from not penetrating and pulling a chip,” Gibbs says, “which allows the blade to skip across the material and chatter. This causes work-hardening of the material, dulling the blade and making the blade walk, and possibly scraping the material by the end.”
Setting the speed
Gibbs notes that the correct blade speed is essential to getting accurate cuts and a quality finish, as well as prolonging the life of the blade. But speed and feed rates go hand-in-hand, he says.
“I always say that it is the ballroom dancing of sawing,” Gibbs says. “If you are off, make a small adjustment starting with the blade speed and then move to adjusting the feed, eliminating the chatter for a smooth quiet movement of the X and Y axes.”
Lenox’s Fernandes agrees, offering that while feed rates represent the depth of penetration of the tooth into the material, speed is the rate at which the blade cuts across the face of the material. Again, he says evaluating the chips can help dial in the right rates.
“Blade speed can lead to faster cutting rates,” Fernandes says, “but it is restricted by machineability of the material and the heat produced by the cutting action. Too high of a blade speed on very hard materials produces excessive heat and can reduce blade life. Inspecting the chips will help determine the optimum speed and feed rate for the cutting application.”
Dan Stumpe, sales manager at DoAll Sawing Products, notes that blade speed needs to be set depending on the type of material being cut. Stainless and high alloys, for example, require slower speeds that allow the blade to do its job. Softer metals, such as aluminum, can be cut “as fast as the saw will go,” he says. However, cutting too fast on hard materials can result in basically grinding the material instead of cutting it.
Kroetch agrees that the blade speed is determined by the material being cut, but also notes two things that will “make or break cold sawing and cut quality, which are the RPM the blade is turning and the number of teeth on the blade.”
Go with the flow
Call it cutting fluid, coolant or lubrication, metalworkers rely on it for several reasons. For some, it doesn’t act as a coolant at all – rather it’s a lubricant that eases the blade through the material while simultaneously flushing out chips. But when using fluids, it’s important that the main ingredient be properly mixed with water. For example, Kroetch says that weak coolant mixed with too much water shortens blade life. He notes that different brands of coolant might require different water-to-coolant ratios, so it’s important to follow product directions.
“Rust indicates weak coolant and can cause problems on a saw,” Kroetch says, “as well as ruin a saw blade by damaging the coating on the blade. The ratio of water to coolant does not change for different materials; however, there are different types of coolants that can be used when cutting stainless steel or other materials.”
DoAll Sawing’s Stumpe says that when heat build-up is an issue, getting the coolant properly flowing on the cut is going to impact the quality of the blade.
“The bottom line is that coolant prolongs blade life,” Stumpe says. “Cutting causes friction and heat and coolant acts as the lubrication and heat reducer to prolong blade life. Without coolant, the chips can ‘weld’ themselves to the blade tips and cause problems in the cut.”
Lenox’s Fernandes agrees, adding that lubrication not only improves blade life and offers more economical cutting, but some fluids are also better at cooling while others are more efficient at lubricating.
“The application needs will determine which fluid is best,” Fernandes says. “With that said, properly applying the fluid to the shear zone can reduce heat and produce good chip flow.”
It’s not uncommon to see a seasoned saw operator place their hand on a machine while it’s running and get a feel for what the saw is doing. They’re letting the vibration of the machine do the talking, and as most saw operators know, the less vibration the better.
“Harmonic vibrations are created when cutting and it is necessary to take all possible steps to minimize the damage done to the fragile teeth tips,” DoAll Sawing’s Schmidt says. “The saw blade industry has taken many steps to try and help. The creation of the multi-pitch blade breaks the vibration at the teeth tips. Manufacturers are using castings in their builds, which act as a sponge and absorb vibrations. Some have even gone as far as filling structural tubes used in the manufacture of their machines with vibration-absorbing materials.”
Fernandes says if there is excessive noise, there is probably excessive vibration. Breaking in the blade can be a major factor in lessening vibration, as well as prolong the life of the blade.
“Vibration causes teeth to chip,” he says, “which can lead to crooked cutting and shorter blade life. To combat vibration, a blade can go through a break-in process. This is important because a new blade typically has very sharp teeth. Honing the teeth to form a micro-fine radius will enable them to withstand chipping and improve blade life. If an operator is experiencing vibration, they should decrease the blade speed and feed rate to form a good chip.”
Kroetch advises cold saw operators to avoid vibration by using sharp blades. Furthermore, using a blade with the wrong number of teeth also leads to encountering more vibration. But blade speed and feed rate also play into the rate at which vibration occurs.
“Most cold saws have two cutting speeds, high or low,” Kroetch says. “In many cases, two speeds are enough, but having a variable-speed drive option allows operators to fine-tune blade speed to the exact RPM needed for their material, thus reducing the vibration.”
Taking every sawing parameter into consideration will not make a difference if the material isn’t properly secured. Whether it’s on one side of the blade or both, securing the material to the saw table will ensure that the cuts are square and the blade lasts as long as it should.
“Not clamping properly is just a waste of time and money,” DoAll Sawing’s Gibbs says. “All it will do is harm someone or lead to a major failure of the machine or blade. It can be costly even if you do make it through without damaging machine components or the operator. What did it do to the material? I would say save yourself the headache and funds – always properly clamp.”
With cold saws, Kroetch says both sides of the material must be clamped at the same time during the cut.
“If the material is only clamped on one side of the blade,” he says, “you’ll end up with a burr on the piece that is not clamped. Burrs require a secondary grinding operation to clean up the cut part – and time is money.”